1. Field of the Invention
The present invention relates to a method of forming a crowned or convex sliding surface in a mechanical part or element as for example a valve lifter, cam follower, rocker arm, valve stem, etc. of an internal combustion engine.
2. Description of the Prior Art
It is known that a sliding surface of a mechanical part is formed into a slightly crowned or convex shape in place of being formed into an exactly planer shape with a view to preventing misaligned contact with a sliding surface to be matched. An example of a crowned sliding surface is so shaped that the central portion protrudes from the peripheral portion by an amount ranging from several um to several tens um.
In the meantime, with a view to improving the wear resistivity, it has recently been practiced to form only the sliding section of a mechanical part from a material having a high wear resistivity as silicon nitride, silicon carbide, sialon, etc., and the remaining section from metal.
In case of forming such a crowned sliding surface in a sliding section made of a material having a high wear resistivity after the baking or firing of the sliding section, a problem of a considerably high cost is encountered. On the other hand, in case of forming such a crowned sliding surface in the sliding section before the baking or firing, another problem of a low dimensional accuracy of the sliding surface is encountered due to the large contraction or shrinkage of the sliding section occuring in case of the baking or firing.